Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$58.87	12.430%	$66.1875	$66.19	$66.20	$66.20
Purchase #2	$130.77	13.284%	$148.1415	$148.14	$148.15	$148.10
Purchase #3	$230.60	5.434%	$243.1308	$243.13	$243.15	$243.10
Purchase #4	$45.60	7.262%	$48.9115	$48.91	$48.90	$48.90
Purchase #5	$78.34	6.606%	$83.5151	$83.52	$83.50	$83.50
Purchase #6	$167.76	3.635%	$173.8581	$173.86	$173.85	$173.90
Purchase #7	$73.89	12.264%	$82.9519	$82.95	$82.95	$83.00
7 purchase totals =	$785.83		$846.6964	$846.70	$846.70	$846.70